A shower leak into the ceiling below: where it is actually coming from

A stain on the ceiling under a bathroom is the usual way a shower leak announces itself, and by then it has normally been going on for a while. The good news is that a shower only leaks from four places, and a little patience will usually tell you which one before anyone opens anything.

The four places a shower leak comes from

• The supply side — the valve and the pipes inside the wall. These are under pressure all the time.
• The drain — the connection where the shower floor meets the waste pipe.
• The pan — the waterproof layer under the tile that is meant to catch everything and send it to the drain.
• The edges — caulk at the door, the corners, and where the base meets the wall.

First clue: does the stain grow when nobody showers?

This one question splits a shower leak in half.

• It keeps spreading even when the shower is not used. That points at the supply side, because only the supply is under pressure all the time. A valve or a fitting in the wall is the usual cause.
• It only appears or grows after showers. Then it is the drain, the pan or the edges — water that is only there while the shower runs.

Two shower leak tests you can do yourself

Both take an afternoon and cost nothing. Do them on different days so you can tell the results apart.

• Spray only the floor. Hold the shower head low and aim it straight at the drain, keeping water off the walls and door. If the ceiling below gets wet, the leak is in the drain or the pan.
• Spray only the walls and the door. If the leak shows up now and not in the first test, it is the edges — failed caulk at a corner or along the door are the common ones.

If you want to be sure about the pan, plug the drain, fill the base with an inch or two of water, mark the level, and leave it for several hours. A drop that is more than evaporation means the pan is letting water through.

Why a shower can look perfect and still leak

Grout is not waterproof. Water soaks through it every time the shower runs, and that is by design — the pan underneath is what is meant to stop it. So a shower with immaculate tile can have a failed pan, and the first sign of that shower leak is the ceiling below.

In older houses here that layer is often lead, formed by hand and dressed into the opening. Newer showers use membranes or liquid coatings. Either way it is invisible once the tile is down, and when it fails the honest fix is taking the floor up rather than sealing over the top.

What not to do about a shower leak

• Do not recaulk over the top and wait to see. If the pan has gone, fresh caulk changes nothing except how long the damage goes on.
• Do not ignore a soft or springy floor around the shower. That is wet subfloor, and it gets worse.
• Do not paint the ceiling stain until the cause is fixed. You will just be painting it again.
• Do not keep using a shower over a ceiling that is sagging. Plaster holding water comes down without much warning.

When to call

Call if the stain keeps growing, if tiles sound hollow or have come loose, if the floor feels soft, if there is a musty smell you cannot get rid of, or if the pan test shows a drop. If the stain grows even when the shower is off, that is a supply leak in the wall and it is worth finding quickly — that is leak detection. Everything else here is shower repair, and we will tell you which of the four it is before anything comes apart.

You can see the kind of work this involves — including the lead pan above — on our work page. If water is actually coming through the ceiling right now, shut it off at the main water shut-off valve first.

KBD Plumbing & Heating works across lower Westchester — Dobbs Ferry, Hastings-on-Hudson, Irvington, Yonkers, White Plains and the rest. Licensed and insured, price agreed before work starts, and the phone is answered any hour including holidays: (914) 233-3000.

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